Highly brominated flame retardant compounds have relatively low bioavailability, but some of these compounds have been shown to be of environmental concern. Tetradecabromodiphenoxybenzene (TDBDPB) contains 14 bromine atoms and is the major component of commercial flame retardant mixtures such as the recently phased out SAYTEX 120. The chemical stability of TDBDPB has not been reported. We demonstrated that TDBDPB can photolytically undergo step-wise reductive debromination that follows first-order kinetic degradation models when exposed to ultraviolet (UV) or natural sunlight radiation, and when dissolved in the solvents tetrahydrofuran, methanol or n-hexane. Photolytic degradation half-lives of TDBDPB ranged from 98 to 169 min, 0.78 to 0.83 min, 1.0 to 1.8 min and 4.9 to 7.4 min when exposed to UV-A, -B and -C and natural sunlight, respectively. However, the TDBDPB half-lives when exposed to UV-B and especially UV-C are likely underestimated since solutions were in borosilicate glass vials during irradiation, resulting from increasingly lower % transmittance of λ < 300 nm. Neat technical TDBDPB powder exposed to UV-B and -C radiation also produced less brominated products, although the rate was much slower as compared to when in solution. Exposure of TDBDPB solutions to natural sunlight generated a number of polybrominated diphenoxybenzene (PBDPB) photolysis products, among which the Br(4) to Br(7) PBDPBs were the most frequently observed and estimated to be most concentrated. As evidenced by the TDBDPB half-lives and the degree of debrominated by-product formation, the findings showed that the fraction of the absorbed irradiation that was of sufficient energy to break C-Br bonds of TDBDPB and lesser brominated PBDPBs increased from UV-B or -C to UV-A. Coincidentally, we recently reported on the presence of several Br(4) to Br(6) methoxylated PBDPBs in the Great Lakes herring gull eggs, which may be linked to a TDBDPB source via photolytic degradation to more bioavailable and persistent debromination products.